1. Field of the Invention
The present invention relates to a supercooling type mist eliminator apparatus applicable to a wet type exhaust gas desulfurization system, a dust-removing system and a dust enlarging system for use in wet type electric dust collectors.
2. Description of the Prior Art
A known wet type exhaust gas desulfurization system for coal burning thermal power is schematically shown in FIG. 4. A wet type exhaust gas desulfurization system (hereinafter abbreviated as "desulfurization system") is a system normally comprising a quenching tower, an absorption tower and an eliminator. In FIG. 4, exhaust gas is introduced through an exhaust gas duct 11 into a gas gas heater 1 (hereinafter abbreviated as GGH heat extractor. After exhaust gas heat has been collected at the GGH heat extractor, the exhaust gas is sent to a quenching tower 2, in which the dust in the exhaust gas is removed by the spraying of coolant water and the exhaust gas is humidified and cooled. Thereafter, the exhaust gas is led to an absorption tower 3, in which SO.sub.2 contained in the exhaust gas is absorbed and removed by an absorbent liquid. Subsequently, after gypsum mist generated in the absorption tower 3 has been removed in an eliminator 4, residual dust in the exhaust gas is removed in a wet type electrostatic precipitator 5 (hereafter abbreviated as WEP). In succession, in another gas gas heater 6 (hereinafter abbreviated as GGH reheater), the exhaust gas is heated and raised in temperature by the heat collected by the GGH heat extractor 1, and then exhausted to the atmosphere through a stack. It is to be noted that the dust concentration in the outlet exhaust gas of the eliminator 4 cannot be reduced to 10 mg/m.sup.3 N or less, because removal of micro-fine particles is difficult in the eliminator. Therefore, in order to reduce the dust concentration in the exhaust gas exhausted to the atmosphere to less than 10 mg/m.sup.3 N, dust is further removed by means of the WEP 5. In addition, for the purpose of removing gypsum mist of the absorption tower 3 which deposits on crimped-plate-shaped elements of the eliminator 4, as shown in FIG. 5, water supplied externally of the system through a pipe 9 is sprayed over the elements through spray nozzles. After having removed the gypsum deposited on the elements, this spray water is fed to the quenching tower 2 through a pipe 10 and serves as supplementary water for the coolant water evaporated and dissipated into the exhaust gas.
In the crimped-plate type mist eliminator known in the prior art, it is difficult to effectively remove dust having a micro-fine particle diameter. In the case of the above-described known desulfurization system, in order to reduce a dust concentration in the exhaust gas at the outlet of the eliminator to 10 mg/m.sup.3 N or less, dust removal is further effected by means of a WEP, resulting in that plant and equipment investment is increased, a large plant site is necessitated and running costs become large.
Also, there is a problem that while the water supplied externally of the system is used for washing out dust or gypsum deposited on the elements of the eliminator and thereafter fed to the quenching tower to serve as supplementary water for a coolant water, since a large amount of water cannot be used for the reason that, as a large amount of water is used, drain water increases, washing of the elements would become insufficient, gypsum would remain on the elements, and, in the worst case, partial blocking may arise.